Fuel injection systems serve for the supply of fuel from a fuel tank of a motor vehicle to an internal combustion engine of the motor vehicle. By way of example, two known fuel injection systems will be explained on the basis of FIGS. 1 and 2.
The fuel injection systems shown in FIGS. 1 and 2 are common-rail fuel injection systems. FIG. 1 illustrates a so-called single-controller system, whereas FIG. 2 illustrates a so-called two-controller system.
Referring firstly to FIG. 1, a common-rail fuel injection system according to the prior art is denoted by the reference sign 1. The fuel injection system has a fuel tank 100 in which fuel is stored. The fuel is delivered out of the fuel tank 100 through a first fuel line 102 to a first fuel pump 104. The first fuel pump 104 is a mechanical pre-feed pump which is driven by a crankshaft 106 and which increases a fuel pressure downstream of the first fuel pump 104. A fuel filter 108 and a fuel temperature sensor 110 are arranged in the first fuel line 102.
From the first fuel pump 106, the fuel is conducted through a second fuel line 112 to a second fuel pump 114. The second fuel pump 114 is a mechanically driven high-pressure fuel pump. The second fuel pump 114 serves to further increase the fuel pressure in a region downstream of the second fuel pump 114. In FIG. 1, the second fuel pump 114 is driven by the crankshaft 106, in the same way as the first fuel pump 104. The region upstream of the second fuel pump 114 is referred to as low-pressure region. A ball-seat volume flow regulating valve 116 and a first check valve 118 are arranged in the second fuel line 112, wherein the first check valve 118 is arranged in the second fuel line 112 downstream of the ball-seat volume flow regulating valve 116. The ball-seat volume flow regulating valve 116 is characterized in that it exhibits no leakage in the closed state. The ball-seat volume flow regulating valve 116 is therefore a leakage-free volume flow regulating valve.
From the second fuel pump 114, the fuel is conducted via a third fuel line 120 into a high-pressure fuel accumulator (common rail) 122. A second check valve 124 and a first throttle 126 are arranged in the third fuel line 120. Furthermore, a fuel pressure sensor 128 is arranged on the high-pressure fuel accumulator 122 for the purpose of monitoring the fuel pressure in the high-pressure fuel accumulator 122.
Fuel from the high-pressure fuel accumulator 122 is conducted via a plurality of injector fuel lines 130 to a respective injector 132 of the internal combustion engine. Each injector fuel line 130 has an associated second throttle 134. Injector leakage from the respective injector 132 is supplied via an injector return line 136 back to the fuel tank 100, wherein a third check valve 138 is arranged in the injector return line 136.
For pressure regulation in the low-pressure region, a pressure regulating line 140 connects the second fuel line 112 to the first fuel line 102. A pressure regulating valve 142 is arranged in the pressure regulating line 140.
As a safety measure, in the high-pressure region, there is provided a high-pressure return line 144 which is connected at one end to the third fuel line 120 and at its other end to the return line 136. In the high-pressure return line 144 there is provided a pressure limiting valve 146 which, in the event of an inadmissibly high fuel pressure in the high-pressure region, permits a return flow of fuel into the fuel tank 100.
Lubrication of the second fuel pump 114 is realized via a lubricant fuel line 148 which is connected at one end to the second fuel line 112 and at its other end to a lubricant inlet of the second fuel pump 114. In the lubricant fuel line 148 there are arranged, in the downstream direction, a third throttle 150 and a fourth check valve 152. The fuel used for the lubrication of the second fuel pump 114 exits the second fuel pump 114 via a lubricant return line 154, which opens out into the high-pressure pump return line and into the return line 136. From there, the fuel flows back into the fuel tank 100.
As already mentioned in the introduction, the injection system 1 described in accordance with FIG. 1 is a so-called single-controller system. In said type of system, the fuel pressure in the fuel injection system is regulated exclusively by means of one volume flow regulating valve. In the embodiment illustrated here, this is a leakage-free ball-seat volume flow regulating valve.
A disadvantage of single-controller systems is that only volume flow regulating valves that exhibit no leakage or little leakage can be used. This will be explained in more detail below with reference to FIG. 2. Furthermore, the use of leakage-free volume flow regulating valves, in particular of ball-seat volume flow regulating valves, is cost-intensive owing to their expensive production.
Another form of a known injection system is denoted in FIG. 2 by the reference sign 2. The fuel injection system 2 has a fuel tank 200 in which fuel is stored. In the fuel tank 200 there is arranged a first fuel pump 202 which is electrically operated and which increases a fuel pressure downstream of the first fuel pump 202. The first fuel pump 202 normally runs continuously in an unchanging manner.
By means of the first fuel pump 202, fuel is delivered out of the fuel tank 200 via a first fuel line 204 to a second fuel pump 206. The second fuel pump 206 is a mechanically operated high-pressure fuel pump which serves to further increase the fuel pressure in a region downstream of the second fuel pump 206. The region between the first fuel pump 202 and the second fuel pump 206 is referred to as low-pressure region. In the first fuel line 204 there are arranged, in a downstream direction, a fuel filter 208, a fuel temperature sensor 210, a slide-type volume flow regulating valve 212, and a first check valve 214. The slide-type volume flow regulating valve 212 exhibits leakage in the closed state, that is to say is leakage-prone.
From the second fuel pump 206, the fuel is conducted via a second fuel line 216 into a high-pressure fuel accumulator (common rail) 218. A second check valve 220 and a first throttle 222 are arranged in the second fuel line 216. Furthermore, a fuel pressure sensor 224 is arranged on the high-pressure fuel accumulator 218 for the purpose of monitoring the fuel pressure in the high-pressure fuel accumulator 218.
Fuel from the high-pressure fuel accumulator 218 is conducted via a plurality of injector fuel lines 226 to a respective injector 228 of the internal combustion engine. Injector leakage from the respective injector 228 is supplied back to the fuel tank 200 via an injector return line 230.
A pressure regulating valve 232 for active pressure regulation is provided in the high-pressure region between the second fuel pump 206 and the injectors 228. The pressure regulating valve 232 is arranged in a line 234 which connects the high-pressure fuel accumulator 218 to the first fuel line 204 between the fuel filter 208 and the first fuel pump 202.
For pressure stability in the low-pressure region upstream of the VCV, a low-pressure return line 236 is provided which is connected at one end to the second fuel pump 206, and via the latter to the low-pressure circuit via the line 240 and the throttle 142, and at its other end to the injector return line 230. In the low-pressure return line 236 there is provided a pressure limiting valve 238 which permits a return flow of fuel into the fuel tank 200.
Lubrication of the second fuel pump 206 is realized via a lubricant fuel line 240 which is connected at one end to the first fuel line 204 and at its other end to a lubricant inlet of the second fuel pump 206. A second throttle 242 is arranged in the lubricant fuel line 240. The fuel used for the lubrication of the second fuel pump 206 exits the second fuel pump 206 via a lubricant return line 244, in which a third throttle 246 is arranged. The lubricant return line 244 opens out into the low-pressure return line 236. From there, the fuel flows back into the fuel tank 200.
Here, regulation of the fuel pressure is realized firstly by means of the slide-type volume flow regulating valve 212 in the low-pressure region, and secondly by means of the pressure-regulating valve 232 in the high-pressure region. Here, the pressure regulating valve 232 actively regulates the fuel pressure in the fuel injection system 2. Said system type is therefore a so-called two-controller system.
The use of two control elements in a fuel injection system having a slide-type volume flow regulating valve is necessary because a mass-produced slide-type volume flow regulating valve exhibits leakage in the closed state. It is therefore the case that in particular small delivery rates of the high-pressure fuel pump cannot be regulated with sufficient accuracy. In particular, even if the slide-type volume flow regulating valve is actuated at 0% in the case of a normally-closed valve or at 100% in the case of a normally-open valve, leakage occurs into a pump chamber of the high-pressure fuel pump or of the second fuel pump. Said leakage is inherent and cannot be prevented in mass production. The leakage behavior has the effect that, even in the case of a closed volume flow regulating valve, fuel continues to be supplied to the high-pressure fuel pump, and the fuel pressure in the high-pressure region is further increased. There is therefore the need for an additional pressure regulation valve to be provided in the high-pressure region in the fuel injection system in order to regulate the high pressure with the required accuracy.
A disadvantage of the two-controller system is thus the need for two control elements for pressure regulation in a fuel injection system. This leads to increased regulation outlay in relation to the single-controller system. Furthermore, said system is also cost-intensive because two control elements and the associated regulation means are required.
DE 10 2008 059 117 A1 discloses a high-pressure pump arrangement. The high-pressure pump arrangement has a pump body which comprises a low-pressure inlet and a high-pressure outlet. Within the pump body there is provided a pressure build-up chamber within which a plunger is mounted in a movable manner and which is connected via a high-pressure valve to the high-pressure outlet. Furthermore, within the pump body, there is provided a suction chamber which is provided with a suction valve. Furthermore, within the pump body, there is provided a suction duct which runs between the low-pressure inlet and the suction chamber. The low-pressure inlet is connected to an electrically regulable pre-feed pump, which is always operated such that a negative pressure is ensured in the suction chamber of the pump. The regulation of the fuel pressure in the fuel injection system is realized by means of a high-pressure regulating valve.
EP 1 195 514 A2 describes a device for controlling the flow from a high-pressure pump into a common-rail fuel injection system of an internal combustion engine. The common rail provides a supply to a number of injectors of the cylinders of the internal combustion engine, and has a supply provided to it by a high-pressure pump, which in turn has a supply provided to it by a motor-driven variable low-pressure pump. The control device has an electronic control unit for receiving signals which indicate the operating state of the internal combustion engine. The suction side of the high-pressure pump has a throttle. The control unit controls the motor-driven low-pressure pump in order to vary the fuel pressure upstream of the throttle between a predetermined maximum value and a predetermined minimum value, in order thereby to regulate the fuel intake of the high-pressure pump within a predetermined range. For pressure regulation, the device also has a pressure regulating valve in the high-pressure region. Likewise, a pressure sensor in the low-pressure region is used for monitoring the fuel pressure in the low-pressure region.
A further method for generating high fuel pressure, and a corresponding system, are described in U.S. Pat. No. 6,230,688 B1. The system comprises a low-pressure pump as a pre-feed pump, by means of which fuel is sucked from a tank and delivered to the inlet side of a high-pressure pump. A part of the fuel supplied by the low-pressure pump is used for the lubrication of the high-pressure pump, wherein a volume flow regulating valve is used for regulation, and a low-pressure sensor is provided in the supply line.
Likewise, EP 1 574 704 A2 describes a further fuel injection system having an electric low-pressure pump. A control means of a fuel injection system regulates an amount of energy of an electric motor in accordance with a sensor signal output by a common-rail pressure sensor means. In this way, the control means control a fuel supply rate of the low-pressure pump. In this way, the power consumption of the electric motor which drives the low-pressure pump can be regulated in accordance with a pressure supply rate of a high-pressure pump. Furthermore, a pressure sensor in the low-pressure region of the fuel injection system is used for monitoring the fuel supply pressure of the low-pressure pump.
A suction pump system for a fuel direct injection system is described in DE 10 2009 004 590 A1. The fuel injection system has a fuel suction pump which supplies fuel to an injection pump. Furthermore, the fuel injection system comprises an accumulator arranged between the outlet of the suction pump and the inlet of the injection pump, and also a control unit which adapts the energy supplied to the suction pump such that a pressure at the inlet of the injection pump lies above a first predetermined value. The control unit shuts off the energy supplied to the first fuel pump if the pressure at the inlet of the injection pump is higher than a second predetermined value.
DE 10 2006 061 570 A1 describes a further fuel system for an internal combustion engine. The fuel system comprises a first fuel pump and a pressure region into which the fuel pump delivers and which is connected to an elastic volume accumulator. Said volume accumulator has a pressure/volume characteristic curve defined by at least two points. A first point is defined by a first volume at a first pressure which is slightly higher than a vapor pressure of the fuel at ambient temperature, and a second point is defined by a second volume and a second pressure in the pressure range corresponding to a maximum pressure. The difference between the first and the second volume corresponds at least approximately and at least to a value by which the volume of the fuel in the pressure region decreases during cooling from a maximum temperature to ambient temperature.
A disadvantage of the fuel injection systems specified above is firstly the required number of components and the resulting complex control. A further disadvantage is the costs that arise therefrom during the use of such fuel injection systems.